Services are provided in which a femto base station (HeNB (Home eNode B)) creates a femtocell and only contract users are permitted to connect to the femto base station. In such services, there are cases where the femtocell is created within a macro cell created by a macro base station (MeNB (Macro evolutional Node B)).
In the case where a macro UE (MUE (Macro User Equipment)) that is not permitted to connect to a femto base station is present within the femtocell, the SINR (signal to interference and noise ratio) of the macro UE may be deteriorated due to the interference from the femto base station.
Such a macro UE is referred to as a “victim UE”, for example. On the other hand, 3GPP (Third Generation Partnership Project) has studied a method of reducing the interference by decreasing the transmission power of a femto base station, for the purpose of improving the SINR of a victim UE. Specifically, assuming that a femto base station receives a signal transmitted from a macro base station and this received signal is low in level, the received power of the victim UE is considered to be also low. Therefore, the transmission power of the femto base station is decreased.
Meanwhile, if the transmission power of the femto base station is decreased when a victim UE is not present, the communication throughput within the femtocell may decrease unnecessarily. In consideration of this situation, a method has been studied of detecting a victim UE and determining whether to decrease the transmission power of a femto base station (for example, refer to Japanese Laid-open Patent Publication No. 2010-283826 and No. 2010-4187). Specifically, the femto base station receives an uplink signal which a victim UE would transmit, and determines whether a victim UE is present or not, on the basis of the received power of the uplink signal.